Electric power system



May 16, 1939. s, MacFARLANE 2,158,136

ELECTRIC POWER SYSTEM Filed Jan. 18, 1937 fly mam-M Patented May 16, 1939 UNITED STATES PATENT OFFI'CE 4 Claims.

My invention relates, generally, to electric power systems, and it has particular relation to the provision of means for interconnecting a source of alternating current and an electric heating device containing a mass of material, the electrical resistance of which decreases with increase in temperature.

In my copending application, Serial No. 109,299, filed November 5, 1936, and assigned to the assignee of this application, I have disclosed an automatic regulator system for maintaining the resistance of a mass of material substantially constant for a purpose that is disclosed in the copending application of Charles F. Ramseyer,

Serial No. 67,868, filed March 9, 1936, and assigned to the assignee of this application. This method relates to the making of mineral wool from coal ashes that are obtained from coal-fired boiler plants and the like. According to this method, an electric furnace is provided for receiving the ash as it comes from the boiler plant for the purpose of controlling its temperature and viscosity in such manner as to facilitate the subsequent blowing of this product into mineral wool by steam issuing from a jet under high pressure or by equivalent means which will transform the molten material into mineral wool. In order to satisfactorily carry out this process, it is essential that the viscosity of the molten ash product be held substantially constant so that a uniform product will result when it is processed to form the mineral wool. The resistance of the molten mass decreases with increase in temperature. The change in resistance is accompanied by a change in the viscosity of the molten mass, and, therefore, its resistance is an indication of the viscosity so that, if the resistance is held constant, the viscosity will also remain constant.

Not only must the resistance of the mass of material be held substantially constant, but also the entire mass must be uniformly heated. A plurality of pairs of electrodes is positioned in the furnace, and the material to be heated is commonly positioned therebetween. If the pairs of electrodes are connected to a common source in parallel circuit relation, there is a tendency for the resistance between the various pairs of electrodes to change due to uneven temperature distribution throughout the mass of the molten material, and, even if equal voltages are applied to all of the electrodes, there is a tendency for some of them to cease carrying current because of the increase in resistance between them. Portions of the material then become colder until finally the only heating takes place in these portions by heat conduction through the material. At the same time, there is a tendency for the current flow between the remaining pairs of elecrodes to increase and to raise the temperature of the material with which they are in contact. 5 Since the resistance of the material decreases with increase in temperature, this results in accumulative action which causes a wide variation in temperature throughout the mass of material being heated and may cause rapid destruction of the electrodes that are subjected to the extremely high temperatures.

In view of the foregoing, an important object of my invention is to energize a plurality of pairs of electrodes used for heating a mass of material commonly placed between them, and the resistance of which varies inversely with the temperature in such manner that substantially uniform heating of the material will result.

Another important object of my invention is to insure a predetermined division of current flow between a plurality of pairs of electrodes energized from a common source that are employed to heat a mass of material common to them all, the resistance of which material decreases with increase in temperature.

An object of my invention is to individually control the voltage applied to each pair of a plurality of pairs of electrodes a-ranged to heat a mass of material commonly placed therebetween to thereby control the flow of current between each pair of electrodes.

Another object of my invention is to commonly control the voltage applied to a plurality of pairs of electrodes that are arranged to be individually energized for heating a mass of material commonly placed therebetween.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiments hereof shown in the accompanying drawing, and it comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the constructions hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawing, in which the single figure illustrates, diagrammatically, one concrete embodiment of my invention.

Referring now to the single figure of the drawing, it will be observed that the reference character Iii designates a source of alternating current, such as a 60-cycle source, that is connected to energize pairs of electrodes H, l2 and I3 that are positioned inside a furnace M for heating a mass of material I5, the resistance of which varies inversely with the temperature. Conductors l5 and I! may be provided for interconnecting the source Ill and the furnace 14. It will be understood that the source of alternating current H3 is shown as a generator merely for the purposes of illustration, since ordinarily between it and the conductors l6 and H a transmission system including transformers and switches will be connected. In order to control the voltage that is applied to the electrodes H, i2 and 13 in the furnace M, a voltage regulator, shown generally at It, is provided, having a stationary winding 59 connected across the conductors l5 and ii and a movable winding 20 connected in series circuit relation with the conductor 11. The movement of the winding 20 relative to the stationary winding l9 will either increase or decrease the voltage that is applied to the electrodes ll, 52 and E3 in the furnace i4, depending upon its position relative to the winding H), as will be readily understood.

With a view to individually energizing each of the pairs of electrodes l l, l2 and I3, transformers shown generally at 2i, 22 and 23 are provided, each having a primary winding 28p, 22p and 23p and a secondary winding 2 is, 22s and 238. Each transformer 2|, 22 and 23 is provided with its own core filo, 22c and 230 on which are wound the primary and secondary windings individual thereto. It will be observed that the secondary windings are individually connected to each of the pairs of electrodes ll, I2 and [3, while the primary windings are connected in series circuit relation. This circuit arrangement causes a substantially uniform flow of current between. each pair of electrodes, since the current flowing through the primary windings Zip, 22p and 2319 is common to all of the secondary windings 2Is, 223s and 23s. The voltage between adjacent pairs of electrodes is maintained substantially the same, and the presence of a high voltage across a pair of electrodes, if there should be an open circuit in the connections thereto, is avoided. If the material l5 being heated tends to cool between one or more of the pairs of electrodes ll, l2 or iii, the resistance between. these pairs of electrodes will increase and the voltage between them will tend to rise in relation to the voltage that is present between the electrodes in contact with the hotter material, thereby causing more power per unit volume of the material to flow in the cooler paths and thus increase the heating, with the result that the temperature is restored to equilibrium. This self-equalizing heating effect between the pairs of electrodes ll, [2 and 53 results from the automatic increase in impedance of the primary winding of the transformer individual to the pair of electrodes having the higher resistance path therebetween. Since the transformers 2|, 22 and 23 have individual cores, there is no direct interaction between the fluxes in these cores, the sole effect in the change in impedance in the primary windings. In this manner, substantially uniform heating takes place throughout the entire mass of material 55 even though it is commonly interposed between the several pairs of electrodes ii, if! and l3.

The voltage that is applied to each of the pairs of electrodes H, [2 and 13 may be adjusted by the taps 2m, 22a and 23a on the primary windings 2 In, 22p and 23p, respectively. Further adjustments may be provided by the taps 2|b, 22b and 23b on each of the secondary windings 21s, 22s and 233, respectively. Either or both sets of taps may be provided, as will be readily understood.

It will now be apparent that a single adjustment of the voltage regulator 18 will cause a simultaneous change to take place in the voltages that are applied to the electrodes H, 12 and i3 in the furnace H3. The relative values of the voltages that are applied to the pairs of electrodes may be adjusted by the individual taps, and the predetermined division. of current will take place because of the provision of the common primary winding to the plurality of secondary windings, each of which is individual to one of the pairs of electrodes.

It will be understood that a larger number than three pairs of electrodes may be employed in the furnace [4. In one embodiment of the invention. that I have constructed, I have employed six pairs of electrodes, each pair of which is individually energized from the secondary windings of six transformers, the primary windings of which are connected in series circuit relation to a source of voltage that is capable of variation from zero to 4600 volts, as by means of the volt" age regulator Hi. The ratio of transformation in the transformers was such that the normal operating voltage averaged about 42 volts between each of the pairs of electrodes.

Since certain further changes may be made in the foregoing described constructions, and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the foregoing description or shown in. the accompa nying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. Apparatus for interconnecting an alternating current source and a plurality of pairs of electrodes arranged and adapted to receive therebetween a mass of material the electrical resistance of which decreases with increase in temperature comprising, in combination, a plurality of transformers each having a core individual thereto and a secondary winding thereon connected across one of said pairs of electrodes, a primary winding on each core, and circuit means for connecting said primary windings in series circuit relation and for energization to said alternating current source, whereby a predetermined division of current flow is effected between said pairs of electrodes and said mass of material is uniformly heated.

2. Apparatus for interconnecting an alternating current source and a plurality of pairs of electrodes arranged and adapted to receive there between a mass of material the electrical re sistance of which decreases with increase in temperature comprising, in combination, a plurality of transformers each having a core individual thereto and a secondary winding thereon connected across one of said pairs of electrodes, a primary winding on each core, means connecting said primary windings in series circuit relation and for energization to said alternating current source, whereby a predetermined division of current flow is effected between said pairs of electrodes and said mass of material is uniformly heated, and a single control means operatively connected to said circuit means for simultaneously adjusting the current flow between all of said pairs of electrodes.

3. Apparatus for interconnecting an alternating current source and a plurality of pairs of electrodes arranged and adapted to receive therebetween a mass of material the electrical resistance of which decreases with increase in temperature comprising, in combination, a plurality of transformers each having a core individual thereto and a secondary Winding thereon oonnected across one of said pairs of electrodes, a primary winding on each core, circuit means for connecting said primary windings in series circuit relation and for energization to said alternating current source, whereby a predetermined division of current flow is effected between said pairs of electrodes and said mass of material is uniformly heated, and a voltage regulator interposed in said circuit means and arranged and adapted to simultaneously adjust the volt age applied across each of said pairs of electrodes.

4. Apparatus for interconnecting an alternating current source and a plurality of pairs of electrodes arranged and adapted to receive therebetween a mass of material the electrical resistance of which decreases with increase in temperature comprising, in combination, a plurality of transformers each having a core individual thereto and a secondary winding thereon connected across one of said pairs of electrodes, a primary winding on each core, circuit means for connecting said primary windings in series circuit relation and for energization to said alternating current source, whereby a predetermined division of current flow is efiected between said pairs of electrodes and said mass of material is uniformly heated, and adjustable means individual to each of said primary windings and arranged and adapted to individually effect the application of different voltages to each of said pairs of electrodes.

RAYMOND S. MACFARLANE. 

